Hitherto, a member in which a terminal (connector) made of copper or a copper alloy (for example, brass) is attached to electrical wires composed of conductors of copper or a copper alloy, which is called a wire harness, has been used as an electrical wiring for movable bodies, such as automobiles, trains, and aircrafts. In weight reduction of movable bodies in recent years, studies have been progressing on use of aluminum or an aluminum alloy that is lighter than copper or a copper alloy, as a conductor for an electrical wiring.
The specific gravity of aluminum is about one-third of that of copper, and the electrical conductivity of aluminum is about two-thirds of that of copper (when pure copper is considered as a criterion of 100% IACS, pure aluminum has about 66% IACS). Therefore, in order to pass a current through a conductor wire material of pure aluminum, in which the intensity of the current is identical to that through a conductor wire material of pure copper, it is necessary to adjust the cross-sectional area of the conductor wire material of pure aluminum to about 1.5 times larger than that of the conductor wire material of pure copper, but aluminum conductor is still more advantageous than copper conductor in that the former has an about half weight of the latter.
Herein, the term “% IACS” mentioned above represents an electrical conductivity when the resistivity 1.7241×10−8 Ωm of International Annealed Copper Standard is defined as 100% IACS.
In order to use the aluminum as a conductor of an electrical wiring of a movable body, the aluminum is produced by cumulation of several techniques, one of which is a technique for producing a stranded wire. Stranded wires are generally classified into two kinds, one of which is obtained by stranding a drawn material, and the other of which is obtained by stranding an annealed material. In either case, even the same material is used, the shape of the stranded wire after stranding differs, depending on the difference in tensile strength (TS), 0.2% yield strength (YS), and elongation (El).
The shape of a stranded wire is determined based on a twist pitch (or a lay length), when a central wire wound with solid wires is stranded or twisted. When the twist pitch is narrow, the state of the strand becomes dense. On the other hand, when the twist pitch is broad, gaps are formed in twist intervals. Further, a problem of stranding is that, when irregularity of stranding, protrusion of stranding, or the like occurs, a failure occurs in the subsequent step, such as a coating step. Furthermore, when such irregularity of stranding, protrusion of stranding, or the like exist, wart-like appearance is confirmed even from the top of a coating. In such a state, a defect called kink is apt to occur, which leads to clogging of an automatic feeding apparatus and the like in a step of assembling a harness, and the like.
Furthermore, a solid wire in an electrical wire that is used in harnesses has a small diameter of 0.3 mmφ or less, and it is not a thick electrical wire as used in overhead electric power transmission lines.
Therefore, it is considered that use of a coated thin electrical wire (solid wire) is one of the features of a conductor that is used in movable bodies.
With respect to such a use, pure aluminum (1000-series) is used in electric power transmission lines in many cases, but it is low in tensile strength and has an insufficient mechanical strength for use in an electrical wire for harnesses. Accordingly, alloying by adding various additive elements has been studied. However, it is also a well-known fact that alloying causes decrease in electrical conductivity. Therefore, 2000-series and 6000-series that are excellent in mechanical strength cannot be used, and other alloy-systems are also not so good.
On the other hand, as aluminum conductors used for electronic wirings of movable bodies, Patent Literatures 1 to 13 mainly describe about wire harnesses for automobiles. It is necessary that an aluminum conductor for harnesses is used in the form of a stranded wire, and thus, mechanical properties that enable readily stranding are desired. Furthermore, the wire diameter thereof is thin as 0.3 mmφ or less, and further the surface thereof is coated. Therefore, such matters are not envisaged in pure aluminum-based materials that are used for electric power transmission lines and electrical power cables, and in the materials described in Patent Literatures 1 to 13. Thus, those materials are not considered to have properties and costs that are required for use in movable bodies.
Specifically, the alloys to which Zr is added, as described in Patent Literatures 1, 3, 4, 8, 11 to 13, and the like, are ones improved in creep resistance, but they have a problem of low electrical conductivity. Furthermore, there is another problem that a heat treatment for a long time period is required for forming an Al3Zr intermetallic compound, which makes control of the process difficult.